The present invention relates generally to a system and method of continuous detonation in a gas turbine engine and, in particular, to a system and method of continuous detonation in a gas turbine engine where a mixture of fuel and air is continuously detonated in at least one helical channel of a rotatable member to form combustion gases having an increased pressure and temperature.
It is well known that typical gas turbine engines are based on the Brayton Cycle, where air is compressed adiabatically, heat is added at constant pressure, the resulting hot gas is expanded in a turbine, and heat is rejected at constant pressure. The energy above that required to drive the compression system is then available for propulsion or other work. Such gas turbine engines generally rely upon deflagrative combustion to burn a fuel/air mixture and produce combustion gas products which travel at relatively slow rates and constant pressure within a combustion chamber. While engines based on the Brayton Cycle have reached a high level of thermodynamic efficiency by steady improvements in component efficiencies and increases in pressure ratio and peak temperature, further improvements are becoming increasingly costly to obtain.
Accordingly, improvements in engine efficiency have been sought by modifying the engine architecture such that the combustion occurs as a detonation in either a continuous or pulsed mode. Most pulse detonation devices employ detonation tubes that are fed with a fuel/air mixture that is subsequently ignited. A combustion pressure wave is then produced, which transitions into a detonation wave (i.e., a fast moving shock wave closely coupled to the reaction zone). The products of combustion follow the detonation wave at the speed of sound relative to the detonation wave and at significantly elevated pressure. Such combustion products then exit through a nozzle to produce thrust. Examples of a pulse detonation engine are disclosed in U.S. Pat. No. 5,345,758 to Bussing and U.S. Pat. No. 5,901,550 to Bussing et al. Simple pulse detonation engines have no moving parts with the exception of various forms of externally actuated valves. Such valves are used to control the duration of the fuel/air introduction and to prevent backflow of combustion products during the detonation process. An example of a rotary valve utilized for pulse detonation engines is disclosed in U.S. Pat. No. 6,505,462 to Meholic. While such pulse detonation configurations have advanced the state of the art, the valves and associated actuators are subjected to very high temperatures and pressures. This not only presents a reliability problem, but can also have a detrimental effect on the turbomachinery of the engine.
Several pulse detonation designs which have eliminated the need for a separate valve, and are also owned by the assignee of the present invention, have been disclosed in U.S. Pat. No. 6,928,804 to Venkataramani et al., U.S. Pat. No. 6,889,505 to Butler, et al., U.S. Pat. No. 6,904,750 to Venkataramani et al., and U.S. Pat. No. 6,931,858 to Venkataramani et al. While each of the aforementioned pulse detonation systems are useful for their intended purpose, the task of creating and controlling a periodic detonation must be addressed, as well as integration of the device into an otherwise steady flow propulsion system. Other obstacles include the prevention of backflow into the lower pressure regions upstream of the pulse detonator, survivability of turbomachinery and ductwork upstream and downstream of the pulse detonator in an axially unsteady flow field, and capability of cooling flows for maintaining a positive gradient during pulses.
Accordingly, it would be desirable for a mechanism to be developed which sustains continuous detonation of a fuel-air mixture within a compact device. In this way, the continuous detonation process serves to significantly elevate the temperature and pressure of the incoming mixture. At the same time, a steady surrounding flow field is promoted, gases upstream and downstream of the device are isolated, and a high enthalpy exit flow ready to do work is produced. It would also be desirable for a continuous detonation system to be developed for a gas turbine engine which is able to operate the engine without the need for a separate valve and without causing adverse effects on the other components of the gas turbine engine. Further, it would be desirable for such continuous detonation system to be adaptable to a gas turbine engine for both aeronautical and industrial applications so as to provide a substitute for a combustor or possibly eliminate the entire core (i.e., a high pressure compressor, combustor, and high pressure turbine).